Sylvia Meagher was a research analyst at the UN’s World Health Organization. She took a strong interest in the assassination of John F. Kennedy and read the twenty-six volumes of the hearings and exhibits of the Warren Commission: "It was appalling to find how many of the Commission's statements were unsupportable or even completely contradicted by the testimony and/or exhibits... I began to list what is now a long list of deliberate misrepresentations, omissions, distortions, and other defects demonstrating not only extreme bias, incompetence, and carelessness but irrefutable instances of dishonesty."
In 1965 Meagher published Subject Index to the Warren Report and Hearings and Exhibits. As Meagher pointed out, studying the entire twenty-six volumes without a subject index would be "tantamount to a search for information in the Encylopedia Britannica if the contents were untitled, unalphabetized, and in random sequence."
A deep study of the Warren Commission Report convinced her that the its detailed evidence contradicted its general conclusions. Meagher therefore published Accessories After the Fact: The Warren Commission, the Authorities, and the Report (1967). Meagher was unconvinced that Lee Harvey Oswald had been a lone gunman and concluded that the Warren Commission had attempted to cover-up details of the real people behind the assassination. Meagher believed that John F. Kennedy had been killed by a group Anti-Castro exiles.
Richard Schweiker, who later became a member of the House Select Committee on Assassinations, pointed out that the Accessories After the Fact: The Warren Commission, the Authorities, and the Report "clearly establish Sylvia Meagher’s major contribution to understanding this tragic incident in our nation’s history... and was instrumental in finally causing a committee of Congress - with full subpoena power, access to classified documents, and a working knowledge of the nuances of the FBI and CIA - to take a second official look at what happened in Dallas November 22, 1963.”